Accelerometers are used for measuring levels of vibration in many different types of machinery. In many applications, such as for example aircraft engines, there is a need for duplicate measurements of vibration level in order to provide a level of redundancy in case of sensor failure.
It is therefore known to use dual channel accelerometers in such redundant applications. Various arrangements of dual channel accelerometer are known.
One such arrangement 10, shown in FIG. 1, employs two single channel accelerometers 12, 14 mounted side by side within a common housing 22. This has the advantage of being simple and is therefore a low cost solution.
However, ensuring that both accelerometers 12, 14 experience the same acceleration in a vibration environment is difficult. One reason for this difficulty is that the two accelerometers 12, 14 must necessarily be spaced apart from one another and thus cannot experience exactly the same vibration.
In addition, twisting or flexure of the baseplate 20 on which the two accelerometers 12, 14 are mounted further exacerbates the difference in vibration input to each of the accelerometers 12, 14. Thus, consistent channel-to-channel matching is difficult to achieve.
An alternative arrangement 30, shown in FIG. 2, is to position the two single channel accelerometers 32, 34 on top of each other. This arrangement has the advantage that both accelerometers 32, 34 now experience the same vibration input. However, differences remain between the vibration inputs to each of the two accelerometers 32, 34.
This is because bending of the accelerometer stack caused by lateral movement of the baseplate 38 causes the upper accelerometer 34 to experience a different vibration input to that experienced by the lower accelerometer 32.